This invention relates to an insulation displacement terminal which can effect stable insulation displacement connection with a conductor comprising a number of fine strands.
For convenience of explanation, a conventional insulation displacement terminal will be described below by referring to the drawings. FIG. 6A is a perspective view of a conventional insulation displacement terminal.
FIGS. 7A and 7B are graphs which illustrate relationships between a slot width and the number of cutoff strands and between the slot width and a contact resistance, respectively.
Heretofore, in order to connect a conductor in an electric cable, for example, a wire harness for an automotive vehicle or the like to a terminal in a manner of insulation displacement connection, an insulation displacement terminal 1, as shown in FIG. 6A, has been used which is provided with a slot 1a having a given slot width WS. The slot 1a in the insulation displacement terminal 1 is provided on an open part with a pair of slopes 1 b each having a wire (electric cable) guide angle a with respect to a longitudinal axis of the slot or a direction of insertion of the electric cable. Such an insulation displacement terminal requires a maximum force when an insulation sheath in the electric cable is stripped. This maximum force is called a stripping force for an insulation sheath.
In a design of the insulation displacement terminal, after a relationship between the wire guide angle a and the stripping force for insulation sheath has been found, the wire guide angle a is selected so that a force applied to the insulation displacement terminal or an insulation displacement tool becomes minimum. In order to maintain stabilization of insulation displacement connection of the conductor, the slot width SW is set so that the strands of the conductor are compressed without causing any cutoff of the strands, so that the strands behave as if they were a single wire as a whole, and so that the contact resistance between the conductor and the insulation displacement terminal becomes stable. That is, as shown in FIG. 7A, the slot width WS is designed so that no cutoff of the strands is caused and the contact resistance is in an allowable area of stabilization.
On the other hand, an electric cable to be used in movable parts in an apparatus which effects a sliding, rotating, or bending motion requires high flexibility. A conductor having a number of fine strands is suitable for satisfying such a requirement (hereinafter referred to a flexible conductor). Such a flexible conductor has a nominal cross sectional area and a number of strands, such as more than fifteen (15) in 0.3 mm.sup.2, more than nineteen (19) in 0.5 mm.sup.2, more than thirty (30) in 0.75 mm.sup.2, more than thirty-seven (37) in 1.25 mm.sup.2, or the like.
However, since the strands of the flexible conductor move irregularly and are not stable as a whole when a load is applied to the conductor, there is a problem in which the contact resistance is not stable, if a inflexible conductor having the same nominal cross sectional area is combined with a flexible conductor in which the contact resistance becomes stable in the slot width WS.
If the slot width WS is set to be narrower in order to make the contact resistance of the flexible conductor stable, a part of the strands are cut at the edges b on the intersections between the slopes 1b each having the wire guide angle a and the flat surfaces of the slot 1a when the conductor is inserted into the slot 1a, and thus the strands are not compressed fully. Consequently, a contact load between the strands or between the strands and the terminal does not become great and ultimately the contact resistance does not remain stable.
Even if the slot width WS is changed to find the stable area of the flexible conductor, as shown in FIG. 7B, the strands move irregularly and become unstable as a whole when the slot width WS is wide, while the stands are cut when the slot width is narrow. Accordingly, there is no slot width WS in which the contact resistance is in the stable area and the insulation displacement connection can not be effected.